wlr_popup->current.geometry.{x,y} are usually zero on initial commit, so
xdg-popups were always unconstrained against the output which contains
the top-left of the parent toplevel.
This commit changes xdg-popups to be unconstrained against the output
which contains the top-left of preliminary popup geometry designated by
xdg-positioner given as an argument of "get_popup" or "reposition"
requests.
See https://gitlab.freedesktop.org/wlroots/wlroots/-/merge_requests/3514
which added support on the wlroots side.
We now re-run popup positioning (for both xdg-shell and layer-shell
popups) when the "reposition" event is received. This allows popups that
change size (such as qmpanel's applications menu) to be positioned
correctly.
xdg-shell v3 also gives the compositor some additional "hints" for popup
positioning (reactive, parent_size, and parent_configure_serial) which
are available but we don't make use of currently.
IMHO it encourages better design (by making dependencies more obvious)
to have source file/header file pairs like view.c/view.h, rather than a
monolithic header like labwc.h with everything in it.
I don't think we need to break up all of labwc.h at once, but maybe we
can start pulling it apart bit by bit as it's convenient.
Also:
- Move "struct border" to ssd.h so that view.h can use it without pulling
in all of labwc.h.
- Add a missing required #include within scaled_font_buffer.h (forward
declaration of "struct font" is not enough).
Support identification of wlr_scene_node role to enable simplification
of codebase including the avoidance of iterating over lists of
layer-surface, menuitems, and so on.
Use node-descriptors for xdg toplevels and popups
